Some build environments do not support symbolic links. This patch
removes the symlinks previously used to build fip_create and instead
copies the relevant header files.
The original motivation for using symlinks was to avoid Trusted Firmware
library headers conflicting with headers in the compiler standard
include path. Copying the header files instead has the same effect.

Like other build artefacts, the copied files are listed in .gitignore.

The distclean targets have also been updated to remove the copies.

Change-Id: Ie8b67bcb133f7f1d660ae93b857950aa15e42b1e